This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The development of plenoptic camera that enable to perform refocusing a posteriori is a hectic research subject. In order to achieve such refocusing, it is needed to perform some shifting and adding operations on several sub-aperture images (that correspond to images of a same scene obtained from different acquisition angles at a same time, a sub-aperture image being also named a viewpoint image), as explained for example in the article entitled “Light Field Photography with a Hand-held Plenoptic Camera” by Ren Ng et al, in the Stanford Tech Report CTSR 2005-02. In order to obtain a sub-aperture image from raw data obtained/acquired by a plenoptic camera, usually the processing which is done consists of obtaining the same pixel under each of the micro-lenses comprised in the plenoptic camera (a micro-lens generating a micro image, also named a lenslet image), and gathering these obtained pixels in order to define a sub-aperture image. However, such processing for obtaining a set of sub-aperture images from raw data is based on the hypothesis that each sensor pixel positioned behind the microlenses array only record one viewpoint pixel image, as mentioned in the Chapter 3.3 of the Phd dissertation thesis entitled “Digital Light Field Photography” by Ren Ng, published in July 2006, due to the fact that the coordinates of the center of a micro-image formed by a microlens have only integer values (i.e. there is a perfect match between a micro image (or lenslet image) and the image sensors/pixels sensors). From a mathematical point of view (and in view of the FIGS. 2 and 3 in the present document), such processing from raw data to a set of sub-aperture images can be formulated as follows:Vn,m[k,l]=Rl,k[m,n]Where Vn,m denotes a sub-aperture image, and Rl,k denotes a micro-image (also noted μ-image), with n∈0, N−1, m∈0, M−1, l∈0, L−1, and k∈0, K−1.
However, it should be noted that the hypothesis previously formulated is not always verified. Indeed, the micro-image Rl,k may be misaligned with the sensor array. Therefore, the sub-apertures images extraction process (such process is also named a demultiplexing process or also a decoding process as detailed in the article “Accurate Disparity Estimation for Plenoptic Images” by N. Sabater et al., published in ECCV Workshop 2014) from the raw data is not as accurate as it should be. Hence, it is necessary to improve the extraction process in order to determine correctly the set of sub-aperture images. In order to solve this issue, a technique described in the document US 2014/0146184 proposes to perform a calibration for correcting the misalignment.
The proposed technique is an alternative to the one of document US 2014/0146184.